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From: Fujii Masao <masao.fujii@gmail.com>
Date: Wed, 8 Apr 2026 12:36:19 +0900
Message-ID: 
 <CAHGQGwH_AAbtsiYDJt65N7_4PJ0CgOJmBEaCq68e5_tcuG_vXw@mail.gmail.com>
Subject: Re: Use SIGTERM instead of SIGUSR1 for slotsync worker to exit during
 promotion?
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Nisha Moond <nisha.moond412@gmail.com>,
	"Zhijie Hou (Fujitsu)" <houzj.fnst@fujitsu.com>,
 shveta malik <shveta.malik@gmail.com>,
	PostgreSQL Hackers <pgsql-hackers@lists.postgresql.org>
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On Wed, Apr 8, 2026 at 11:39=E2=80=AFAM Fujii Masao <masao.fujii@gmail.com>=
 wrote:
>
> On Tue, Apr 7, 2026 at 12:48=E2=80=AFPM Amit Kapila <amit.kapila16@gmail.=
com> wrote:
> > I agree with this line of reasoning here or in general as well but
> > personally I am a bit hesitant to back patch changes which are not
> > mandatory. In this particular case, I don't see any problem with
> > backpatching the part of code you want to backpatch, so I leave it to
> > your judgement.
>
> Thanks for the comment!
>
> I decided to backpatch commit 1362bc33e02. Although pg_sync_replication_s=
lots()
> lacks retry logic in v17 and v18 and is therefore less likely to block
> promotion, the issue still exists in those versions.
>
> Given that, it seemed worthwhile to backpatch the change and fix cases wh=
ere
> both the slotsync worker and pg_sync_replication_slots() can block promot=
ion
> when stuck in a wait.
>
> I've pushed and backpatched the patch. Thanks!

The backpatch added PROCSIG_SLOTSYNC_MESSAGE in the middle of enum
ProcSignalReason, which could break the ABI. I=E2=80=99m planning to move i=
t to
the end of the enum in v17 and v18.

That seems to work for v18. However, in v17, NUM_PROCSIGNALS is defined
as the last enum value:

            NUM_PROCSIGNALS /* Must be last! */
        } ProcSignalReason;

So simply moving PROCSIG_SLOTSYNC_MESSAGE to the end would change the meani=
ng
of NUM_PROCSIGNALS.

One option might be to remove NUM_PROCSIGNALS from the enum, move
PROCSIG_SLOTSYNC_MESSAGE to the end, and define it separately, e.g.
#define NUM_PROCSIGNALS (PROCSIG_SLOTSYNC_MESSAGE + 1). Would that
be acceptable without breaking the ABI? Thoughts?

Regards,

--=20
Fujii Masao